The present invention relates to electronic control systems for use in automotive vehicles, and more particularly to a method and apparatus for diagnosing the operation of electronic control systems for vehicles of the type which include a sensor assembly for detecting movement of the vehicle and are arranged to be operated in relation to an electric signal from the sensor assembly.
For example, an engine automatic control system for automotive vehicles has been proposed in which the engine is automatically driven in response to operation of a starting mechanism for effecting start of the vehicle to maintain the engine rotation while the vehicle is moving and the engine is automatically stopped when the vehicle stops moving, both operations being carried out without operating the ignition switch. In such engine automatic control system, motion of the vehicle is detected by a speed sensor assembly such that the engine control circuit operates responsive to changes in amplitude of a speed pulse signal from the sensor assembly.
In operation of the control system, it is, therefore, presumable that if the speed sensor assembly is out of order due to failure in its contact to a connector, disconnection or erroneous earth in its wiring or the like prior to start of the vehicle, the engine is automatically stopped during travel of the vehicle, resulting in unexpected trouble for the operator. In this respect, it is difficult to inspect presence of an error in operation of the speed sensor assembly in its assembled condition in such a way to run the vehicle in a manufacturing or service factory. It is also difficult for the operator to inspect an error in operation of the speed sensor assembly when involved in such unexpected trouble as described above.